Fluoropolymers represent a class of compounds having noteworthy properties for a large number of applications, from painting or special coatings to sealing joints, via optics, microelectronics and membrane technology. Among these fluoropolymers, copolymers are particularly advantageous due to their diversity, their morphology, their exceptional properties and their versatility.
Electroactive fluoroterpolymers, generally used in the form of films, of deposits or of stacks, combined with electrodes, have noteworthy electromechanical properties. They have a high electromechanical energy density. Thus, when devices comprising such terpolymers are subjected to an electric field, they become strained, which makes possible the production of actuators.
The document U.S. Pat. No. 6,787,238 describe the preparation of terpolymers according to a method for the polymerization of a mixture of three monomers comprising a vinylidene fluoride (VDF) monomer, a monomer such as tetrafluoroethylene (TFE) or trifluoroethylene (TrFE) and a monomer such as tetrafluoroethylene (TFE), vinyl fluoride, perfluoro(methyl vinyl ether), bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene (CTFE) and hexafluoropropylene (HFP).
The document U.S. Pat. No. 6,355,479 describes the preparation of terpolymers of vinylidene fluoride, of trifluoroethylene and of a comonomer, such as CTFE or HFP, according to a copolymerization process controlled by means of borane compounds in the presence of oxygen.
The document U.S. Pat. No. 5,087,679 describes the preparation of a dielectric terpolymer which comprises vinylidene fluoride, trifluoroethylene and chlorotrifluoroethylene.
The document U.S. Pat. No. 4,554,335 describes a dielectric polymer material composed of vinylidene fluoride, of trifluoroethylene, of chlorotrifluoroethylene and of another fluorine-containing monomer.
The paper High Electromechanical Responses in a Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) Terpolymer by Xia et al., published in Advanced Materials, 14, 1574-1577 (2002), shows the importance of a third monomer for influencing the microstructure of the copolymer of vinylidene fluoride and of trifluoroethylene.
The paper Influencing dielectric properties of relaxor polymer system by blending vinylidene fluoride-trifluoroethylene-based terpolymer with a ferroelectric copolymer by Casar et al. in Journal of Applied Physics, 115,104101 (2014), describes the mixture of a relaxor terpolymer P(VDF-TrFE-CFE) and of a ferroelectric polymer P(VDF-TrFE).
Likewise, the paper A polymer blend approach to tailor the ferroelectric reponses in P(VDF-TrFE) based copolymers by Chen et al. in Polymer, 54, 2373-2381 (2013), also describes the mixture of a terpolymer and of a copolymer.
The document WO 2011/008940 describes the mixture of a terpolymer and of another fluoropolymer. The document EP 0 206 926 describes mixtures of fluoropolymers or fluorocopolymers.
Finally, the document WO 2014/170479 describes mixtures of a terpolymer P(VDF-TrFE-CFE) or P(VDF-TrFE-CTFE) with a plasticizer of phthalate type, and their use to manufacture films and actuators. It is set out that these mixtures exhibit an improved dielectric permittivity.
However, these mixtures exhibit a poor ecotoxicological profile, the phthalate plasticizer used being toxic. Furthermore, the present inventors have found that the phthalate plasticizer exhibits a tendency toward release (or sweating), which represents a risk for the health, makes difficult the deposition of electrodes and can result in a significant deterioration in the mechanical properties of the films obtained.
There thus exists a need to develop a composition which exhibits good electromechanical properties (in particular for use in actuators), which has a satisfactory ecotoxicological profile and which does not exhibit a risk of release.